March 4, 2019

In 1963, one of the most disastrous rockslides ever to occur, slid into the reservoir behind Vajont Dam in Italy, causing a massive wave to overtop the dam, destroying entire villages and causing more than 2,000 fatalities. Because of the magnitude of the event, the Vajont Dam incident is one of the most researched rockslides in the world, analyzed in technical papers, books and film. This case study can remind us of the hazards that exist at dams, even if a structure is considered safe and does not fail. In the years before the incident, the risk of a major rockslide and its consequences were normalized and as the event was proceeding, a clear, concise warning message was never issued. Vajont highlights the need for thorough geotechnical investigations during dam design, specifically reservoir slope stability analyses. Vajont Dam remains in place today and provides a unique and important educational opportunity for visitors. Compared with historic dam failure and incident case studies, Vajont is unique is many aspects, including:

• Vajont Dam did not fail and remains one of the highest dams in the world,

• The scale of the 1963 rockslide and resultant flood are unprecedented,

• Resultant flooding from the rockslide reached the population at risk almost immediately,

• The fatality rate is among the highest recorded dam failure or dam incident,

• Voluminous research has been conducted on the Vajont rockslide and surrounding geology since the incident.

The field of “human factors” considers how and why systems meet or don’t meet performance expectations, with an emphasis on understanding and prevention of incidents and failures. The systems considered in human factors work, such as dams, typically include both human and physical aspects, and are sometimes referred to as “sociotechnical” systems. To prevent future dam failures, it is essential that dam safety professionals understand both physical factors and human factors, and how they contribute to failures or safety.

Thumbnail Photo: In 2017, the service spillway of Oroville Dam in California, the tallest dam in the US, failed to due to uplift of the slab and subsequent foundation erosion. This was followed by erosion and headcutting at the emergency spillway, which was used for the first time in its history during the incident, and prompted evacuation of about 188,000 people. A wide range of human factors contributed to the incident at individual, organizational, regulatory, and industry levels, starting with the design and construction of the project in the 1960s until the incident in 2017. (Photo Source: Irfan A. Alvi)